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Old 13-02-2015, 13:51   #1
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How Do I Use Slack Tide?

Hello all.

I would love to hear you all describe how you use a slack tide to your advantage.

Currently, I am moored in the south end of Puget Sound. Tacoma to be exact.

All explanations are welcome.

Thanks!

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Old 13-02-2015, 14:03   #2
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Re: How Do I Use Slack Tide?

To do diving, stops you being swept off the wreck.

Slack can be useful to get into a position so you can make most of the tide when it starts to run. Leaving a little early so to make full use of the tide. Can make a huge difference if you time it correctly.
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Old 13-02-2015, 14:30   #3
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Re: How Do I Use Slack Tide?

pretty important to know when slack water is if entering or leaving lagoons through narrow passes as currents can be very strong half an hour either side of slack water.

the same goes for entering large landlocked bodies of water with big tidal ranges.

navigating tidal easturies,like the thames or the Bristol channel ships have for centuries relied on being carried upstream by the flood,and anchoring or mooring up at slack whilst the tide rushes out again,then carry on upstream again with the next flood.
this is how the romans and vikings first colonised the heart of England.
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Old 13-02-2015, 14:41   #4
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Re: How Do I Use Slack Tide?

Slack is not always the same as "time of zero current", esp as you get around Pt. Townsend. The current may change an hour or two behind slack. And the current may be different across the sound. Lots to learn...
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Old 13-02-2015, 14:46   #5
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Re: How Do I Use Slack Tide?

Quote:
Originally Posted by s/v Beth View Post
Slack is not always the same as "time of zero current", esp as you get around Pt. Townsend. The current may change an hour or two behind slack. And the current may be different across the sound. Lots to learn...
that's why you have tidal diamonds on charts and tidal atlass tables so you can calculate tidal current at a given point at any state of the tide.

slack water" is " allways slack water when the water stops moving at a given point,you are confusing "high water slack" and "low water slack" with local slackwater,which do not nessacaraly correspond
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Old 13-02-2015, 14:57   #6
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Re: How Do I Use Slack Tide?

I guess I should have been more specific. How can I use the slack tide, slack water, to my advantage as I leave and return to the dock? Does this information apply more to the docking and leaving or to the actual voyage itself?
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Old 13-02-2015, 15:18   #7
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Re: How Do I Use Slack Tide?

Bobby,

First you have to know when slack water at your dock happens. Then dock at that time.

It is cool, sometimes, to use the flow through a marina to help set you down onto your finger, with contrary breeze. Obviously you need to observe what happens there at your slip.

What we do for docking, is to have a made up line that reaches from our amidship cleat to the stern of the boat, and I get off with it and pop the other eye over the aft-most cleat in the slip, then Jim can steer the boat and keep it close while I get the stern line on, and then the bow lines. Best to put the windward bow line on first, so the boat lies in the slip the way you want her to.

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Old 13-02-2015, 15:18   #8
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Re: How Do I Use Slack Tide?

Quote:
Originally Posted by Bobby Wandering View Post
I guess I should have been more specific. How can I use the slack tide, slack water, to my advantage as I leave and return to the dock? Does this information apply more to the docking and leaving or to the actual voyage itself?
it would depend on the amount of current flowing ,and direction of it passing your dock.

to gain any advantage you want slack water for manoevering on and off the dock,and current with you in your direction of travel.


for example if I were leaving southend and heading to tower bridge on the thames if I left at slack LW I would have about 5 hours of tide flowing at 3-4 knots for the 28 miles upstream voyage,meaning I would only need about 3knots of boat speed to make it there by HW slack.
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Old 13-02-2015, 15:26   #9
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Re: How Do I Use Slack Tide?

Quote:
Originally Posted by Bobby Wandering View Post
I guess I should have been more specific. How can I use the slack tide, slack water, to my advantage as I leave and return to the dock? Does this information apply more to the docking and leaving or to the actual voyage itself?

finding the actual time of slack water at a given point is really easy.

you just need to calculate the time difference between 2 tidal stations on a given stretch of coast,and divide the time difference by the distance from the 2 points
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Old 13-02-2015, 15:46   #10
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Re: How Do I Use Slack Tide?

My much bigger concern is to time my travel so the current squirts me in the direction I want to go. Just this afternoon - Dent - Green Point - Wellbore. We left Squirrel Cove this morning. Will be in Port Neville tonight. Not a prayer of doing that at our normal 6.5 but with the current easy peasy. I wouldn't try that on spring tides but today we were seeing from 1 to 5 knot boosts which we can easily manage.

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Old 13-02-2015, 17:43   #11
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Re: How Do I Use Slack Tide?

Quote:
Originally Posted by atoll View Post
that's why you have tidal diamonds on charts and tidal atlass tables so you can calculate tidal current at a given point at any state of the tide.

slack water" is " allways slack water when the water stops moving at a given point,you are confusing "high water slack" and "low water slack" with local slackwater,which do not nessacaraly correspond
Sorry Atoll,
Here in the PNW slackwater is said to mean Low tide or high tide. In the Salish sea they are often not even close. That was the point I was trying to make.
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Old 13-02-2015, 21:39   #12
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Re: How Do I Use Slack Tide?

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Sorry Atoll,
Here in the PNW slackwater is said to mean Low tide or high tide. In the Salish sea they are often not even close. That was the point I was trying to make.
the point I was trying to make was that,your LOCAL HW slack is able to be calculated with reasonable accuracy.

looking at google maps, it is pretty obvious that hw at Victoria is not going to be at the same time as HW vancoover,or HW seattle

since you have 18 tidal stations to help you working out your local HW forecasting should be able to be done with some accuracy even in the salish sea.

here is a good article discussing your local tides


Pacific Northwest Boating News: Understanding Northwest tides and currents: Part 1 (the ups and downs) | Three Sheets Northwest

Tides are the vertical movement of water, while currents are its horizontal movement. Tides are caused by the gravitational pull between the moon, sun and Earth. Today’s tide may not be the same as yesterday’s tide, and tomorrow’s tides will be different too. The tidal variations are caused by the shifting positions and distances of the moon and sun from the Earth.

Twice each month, around the new moon and full moon, when the Earth, sun and moon are nearly in line, there is an increase in the average range of the tides — higher high tides and lower low tides. These are called “spring tides.” Tides can also be impacted by the shape of the shoreline and the weather.

The Pacific Northwest has “mixed semidiurnal tides,” which means we have two tides daily and the first tidal cycle will be different from the second. Every 24 hours and 50 minutes, there are two high tides and two low tides. Tides tomorrow will be 50 minutes later than tides today.

Generally, high tides occur about 12:25 apart and it takes 6:12:30 for water to shift from high tide to low tide. And tides differ throughout Puget Sound and the Salish Sea – for example, tides in Olympia are roughly 50 minutes later than in Seattle because of the Tacoma Narrows. And Olympia area tides can be more extreme, with higher highs and lower lows than the Seattle area.

In Port Townsend, for example, the average high tide is around seven feet, while in Olympia it is about 13.5 feet — more than a six-foot difference!

Since tides occur at different times and have different highs or lows throughout Puget Sound, there are 18 “tide reference stations” in the region where tides are calculated. Tide books and many Internet resources are based on these tide reference stations. Additionally, there are numerous “subordinate tide reference stations” at which no routine tidal prediction is made. Instead, the average time and height differences between the reference station and that subordinate location can be used to determine local conditions near the secondary station.
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Old 13-02-2015, 23:23   #13
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Re: How Do I Use Slack Tide?

The best tide and current charts in the PNW are the Canadian issues as they cover the currents and High and Low water with enough reference stations to figure things out. However they are all in Standard time so don't forget or things may get exciting. Slack water can be useful for docking, is really important up here for diving but I think the real thing to concentrate on is using the current to your advantage. For example, leaving Port Townsend with the out going current along the Whidbey Island shore with enough time to wind up off Partridge Point for the incoming tide to keep taking you North into the San Juans. 2 different tides helping you go the same direction... It happens again up in the North end of Desolation Sound and off Quadra Island by Seymour Narrows as the incoming tide flows South from around the North end of Vancouver Island down Johnstone Straight instead off up Georgia. All part of the fun. Going against the current is like running up hill so timing is key. If you are Based in Tacoma go play in the Narrows to sort things out. I remember the triumph of sailing under the bridge against the current having missed the tide.
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Old 14-02-2015, 09:47   #14
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Re: How Do I Use Slack Tide?

hmmm...how to use slack tide, etc? more important, is how to use tidal current! it`s like asking 'how high is the sky?', as in getting thru the tacoma narrows, following the correct shorline configuration, etc, against or with the current...clyde
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Old 14-02-2015, 09:58   #15
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Re: How Do I Use Slack Tide?

You do want to hit the passes up North such as Seymor Narrows at slack water to avoid the currents, again a current table is needed because of the differences from high and low water. In the Gulf's Dodd Narrows and the passes out to Georgia etc....

Clyde is right in that shoreline contour can create localized current reversals or "back eddies". Good to learn about for bucking the tide.
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